when you get XP-drained enough to drop a CL, if you drink a RLL you'll restore any drained stats too, as if you had levelled.

Not a bug, this is intentional.

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“We're more of the love, blood, and rhetoric school. Well, we can do you blood and love without the rhetoric, and we can do you blood and rhetoric without the love, and we can do you all three concurrent or consecutive. But we can't give you love and rhetoric without the blood. Blood is compulsory. They're all blood, you see.”
― Tom Stoppard, Rosencrantz and Guildenstern are Dead

Has anyone really made a statement on that one way or another? IMO this is a bug; players should not be encouraged to go through a weird song and dance in order to sidestep an important aspect of gameplay (viz. playing with drained stats).

I mean, it's been around for awhile, but that doesn't mean it's not a bug, just that the devs haven't prioritized it.

Well, maybe. But the thing that bugs me isn't that it's unintended, it's that it encourages this weird little song and dance that isn't itself actually interesting gameplay. Go find a harmless experience drainer, let it beat on you until you lose a level, drink an RLL potion (infinitely available from the temple), and your stats are restored.

In other words, we've replaced townscumming for stat restore potions with townscumming for RLL and finding a weak undead monster. It's arguably an improvement in that most players aren't going to bother, but it should still be fixed. Only get the stat restore the first time you reach a CL.

Please consider the ironman scenario too. Those pots are not so common

+1 here. I've been in a lot of ironman games without a way to restore stats for a very long time. I just keep playing, but if someone wants to waste valuable experience and time by draining to restore stats, then let them.

__________________
“We're more of the love, blood, and rhetoric school. Well, we can do you blood and love without the rhetoric, and we can do you blood and rhetoric without the love, and we can do you all three concurrent or consecutive. But we can't give you love and rhetoric without the blood. Blood is compulsory. They're all blood, you see.”
― Tom Stoppard, Rosencrantz and Guildenstern are Dead

Please consider the ironman scenario too. Those pots are not so common

You'll live. Ironman is supposed to be hard. Plus, if you're having trouble with a particular stat, you can carry around potions that boost that stat (e.g. Potion of Brawn or Potion of Strength). They restore the stat before they boost it. The +1/-1 potions show up when players are still leveling up quickly, and later when leveling tails off, stat potions start becoming a bit more common to compensate. You'll still have to deal with drained stats for a little while if you don't carry the potions with you, but that shouldn't be the end of the world.

Stat-boost potions are a much more sensible method to deal with drained stats than the RLL dance.